a) Field of the Invention
The present invention relates to an IC socket which is applicable to both PGA (pin grid alley) type and LGA (land grid alley) type IC packages.
b) Description of the Prior Art
It is known that IC sockets are used for electrically connecting IC packages to printed circuit boards. However, it is necessary to prepare IC sockets which are to be used exclusively with the PGA type and the LGA type IC packages respectively since these IC packages have leads which are different in shapes thereof.
Illustrated in FIG. 1 is a PGA type IC package 1. This IC package consists of a main body 1a and a plurality of slender leads 1b. FIG. 2 exemplifies an IC socket which is configured for use with the PGA type IC package (disclosed by Japanese Patent Preliminary Publication No. Sho 58-150281). A lever 3 is pivoted to a main body 2 of the IC socket. A cover plate 4 which has a plurality of through holes 4a is slidably attached to the main body 2. Relationship for establishing electrical connection between contact pins 5 disposed on the main body 2 and the leads 1b is illustrated in a partial perspective view presented as FIG. 3, wherein only the through holes 4a are shown with the cover plate 4 omitted. Each of the contact pins 5 is disposed in a hole 2a formed in the main body 2 and has three contacts 5a, 5b and 5c.
For setting the PGA type IC package on the main body 2 of the IC socket described above, the leads 1b are inserted into the through holes 4a as illustrated in FIG. 3, wherein the leads 1b have not been yet brought into contact with the contacts 5a, 5b and 5c of the contact pins 5. When the lever 3 is rotated in a direction indicated by an arrow A in FIG. 2, the cover plate 4 is slid in a direction indicated by another arrow B. Accordingly, the leads 1b are moved by the through holes 4a, and firmly clasped by the contacts 5a, 5b and 5c, whereby the leads 1b are electrically connected to the contact pins 5.
Under the present circumstances, the leads on the IC packages are arranged at narrow pitches and manufactured thinner. Further, materials having low electrical resistance are selected for manufacturing the leads so that the IC packages will consume less electric power, and mechanical strength of the leads 1b tends to be lower. Due to the structure of the contact pins 5, however, the IC socket which is configured as described above hardly allows the holes 2a to have a smaller size, thereby posing a problem that the contact pins 5 can hardly be distributed at narrow pitches on the main body 2. Furthermore, there remains another problem that the leads 1b are bent or injured when they are brought into contact with the contacts 5a, 5b and 5c.
FIG. 4(a) shows an LGA type IC package 6. A lead 6b has a surface which is square, Flat and protrudes slightly from a main body 6a. FIG. 5 exemplifies an IC socket for use with the LGA type IC package (disclosed by Japanese Utility Model Preliminary Publication No. Hei 5-20206). Attached to a main body 7 of the IC socket is a floating plate 8 with a bolt 9 which allows vertical movement of the floating plate 8. A coil spring 10 urges the floating plate 8 upward. The floating plate 8 has a guide 8a mounted thereon and a plurality of through holes 8b formed therein. An intermediate plate 11 has a plurality of through holes 11a and is kept free from the main body 7. A plurality of wire-like contact pins 12 pass through the through holes 11a and have ends 12a which are located in the through holes 8b when an IC package 6 is not mounted on the IC socket. A cover 13 is attached to the main body 7 by a means which allows vertical movement of the cover and is urged upward by a coil spring 14. A link 15 is pivoted by a shaft 15a and has an end connected to the cover 13. Further, a holding means 15b is pivoted by a shaft 15c of the link 15. A locating board 16 which is to be mounted on a printed circuit board is disposed so as to be vertically movable relatively to the main body 7 and the other ends 12b of the contact pins 12 pass through a plurality of through holes 16a.
For setting the LGA type IC package 6 on the IC socket described above, the cover 13 is pushed down against elasticity of the spring 4. Upon pushing down the cover 13, the link 15 and the holding means 15b are moved from locations traced in the solid lines to the locations traced in the dashed lines. In this condition, the IC package 6 is mounted on the floating plate 8. A location of the IC package 6 is determined by the guide 8a. When the cover 13 is free from the pushing down force while keeping the IC package 6 in a condition where it is slightly pushed down, the cover 13 moves upward, whereby the link 15 and the holding means 15b return to the locations traced in the solid lines. Accordingly, the IC package 6 is set and held in position by the holding means 15b. In this condition, the floating plate 8 is slightly pushed down against the elasticity of the coil spring 10, whereby the ends 12a of the contact pins 12 attain to upper ends of the through holes 8b and are electrically connected to the leads 6b of the IC package 6. Though the contact pins 12 are flexed in this condition, they are free from undue stress and cannot be broken owing to the fact that the intermediate plate 11 is movable in the horizontal direction. Further, the through holes 11a serve for preventing the contact pins 12 from mutual contact thereof.
The IC socket for the LGA type IC package, which has the structure described above and uses the wire-like contact pins, exhibits a merit that it allows the contact pins 12 to be disposed at very narrow pitches on the floating plate 8. When the above-mentioned PGA type IC package is mounted on the IC socket which has the structure described above, however, it is very difficult to establish electrical connection securely between all of the leads 1b and the contact pins 12 due to the fact that the leads 1b and the contact pins 12 are thin. Attempts which were made to use thick contact pins 12 posed a problem that the leads 1b were injured due to a high contact pressure which was produced by flexing the contact pins 12.